1. Field of the Invention
The present invention relates to a test-write method, and an information recording method and apparatus for recording information by injecting energy into a recording medium to form a mark different from an unrecorded portion.
2. Background Art
Test writes are performed in order to record information on an optical disc with high accuracy. A test write refers to the operation of determining optimal recording parameters depending on the immediate ambient temperature and the characteristics of the laser mounted on a drive so that a recording mark with better quality can be formed. In optical discs such as DVD-RW, DVD+RW, and BD-RE, a material with a so-called eutectic composition is used in the recording film. In the currently commercially available recording apparatuses, when performing a test write in the aforementioned optical discs, the recording conditions written in the optical disc beforehand are read out and then the laser power is adjusted. The recording conditions include laser power set values, such as a recording power level (Pw) which is of high laser power, an erasing power level (Pe) which is of intermediate power, and a bias power level (Pb). The recording conditions further include various pulse widths of pulses forming a multi-pulse waveform, including a first pulse, a plurality of subsequent intermediate pulses, and a last pulse.
In an actual test write, a technique is used whereby, based on these recording conditions, the ratio of Pw and Pe that are written in the optical disc in advance is fixed, and the optimum recording conditions are determined using the laser power as a parameter. This method is called an Optimum Power Control (OPC). In relatively slow-speed recordings, such as BD 1× speed or DVD-RW 2.4× speed, good recording quality could be obtained by performing a test write by varying only the laser power with a constant Pw/Pe ratio.
Research and development of high-speed recording and reproduction technology for the aforementioned optical discs are progressing. For example, in Optical Data Storage 2003, Proceedings of SPIE Vol. 5069 (2003), p. 130 (Non-Patent Document 1), there is described a recording technique involving a recording speed of 216 Mbps, which corresponds to BD 6× speed. As the recording speed increases, there has also been an advance in the study of recording waveforms suitable for higher speeds, or the so-called 2T-based strategy. The 2T-based strategy involves a recording waveform such that the number of recording pulses is the same for an adjacent pair of even-number length mark and odd-number length mark. For example, as shown in FIG. 2, in a case where a minimum mark length is 2T, a single pulse is generated for a 2T mark and a 3T mark, and two pulses consisting of a first pulse and a last pulse are generated for a 4T mark and a 5T mark. For a 6T mark and a 7T mark, a total of three pulses, namely a first pulse, one intermediate pulse, and a last pulse, are generated.
An example of the 2T-based strategy is disclosed in JP Patent Publication (Kokai) No. 9-134525 A (1997) (corresponding to U.S. Pat. No. 5,732,062; Patent Document 1). The example relates to a multi-pulse recording method using a first pulse, a plurality of subsequent intermediate pulses, and a last pulse, wherein, when recording either an even-number length mark or an odd-number length mark relative to a recording channel clock period, the pulse width of the first pulse and that of the last pulse are made substantially equal to the recording channel clock period.
In another example, JP Patent Publication (Kokai) No. 11-175976 A (1999) (corresponding to U.S. Pat. No. 6,256,277; Patent Document 2) discloses a technique using a recording waveform such that a minimum pulse width in the multiple pulses is set to be larger than one half the window margin. By so doing, the publication reads, a sufficient cooling time for the recording medium can be ensured and the frequency component in the laser drive current can be reduced, so that marks can be formed with sufficient accuracy even at high transfer speeds.
JP Patent Publication (Kokai) No. 2003-30833 A (Patent Document 3) discloses a recording technique whereby not only is the period of intermediate pulse strings made longer than the recording channel clock period, as in JP Patent Publication (Kokai) No. 11-175976 A (1999), but also the edge position of the first pulse and that of the last pulse are varied depending on a preceding space or a subsequent space. The publication states that this method can minimize the edge shift due to thermal interference in a track direction, which poses a problem in a high-density and high-transfer rate recording, and allows a high-accuracy recording control to be realized.
JP Patent Publication (Kokai) No. 2001-331936 A (corresponding to U.S. 2001/053115 A1; Patent Document 4) discloses that the reference clock is displaced for an even-number code sequence and an odd-number code sequence, and that, for even-number and odd-number recording pulse waveforms, the duty ratio of the first pulse and the last pulse is changed between even numbers and odd numbers.
The recording mark-shape controlling effect of the 2T-based strategy in high-transfer rate recording is described in Optical Data Storage 2000, Proceedings of SPIE Vol. 4090 (2000), p. 135 (Non-Patent Document 2), for example.    [Patent Document 1] JP Patent Publication (Kokai) No. 9-134525 A (1997)    [Patent Document 2] JP Patent Publication (Kokai) No. 11-175976 A (1999)    [Patent Document 3] JP Patent Publication (Kokai) No. 2003-30833 A    [Patent Document 4] JP Patent Publication (Kokai) No. 2001-331936 A    [Non-Patent Publication 1] Optical Data Storage 2003, Proceedings of SPIE Vol. 5069 (2003), p. 130    [Non-Patent Publication 2] Optical Data Storage 2000, Proceedings of SPIE Vol. 4090 (2000), p. 135